HOUSTON -- A chemical release sickened dozens of workers at the Valero refinery in the Houston Ship Channel Wednesday, KPRC Local 2 reported.

The Houston Fire Department responded to the sulfur dioxide release at the refinery on Manchester Street near 97th Street at about 9:25 a.m.

More than 2,000 workers were evacuated to Hartman Park.

"No questions -- just go," a worker said.

"We immediately activated our emergency response team. We notified the regulatory agencies," said Fred Newhouse, a Valero spokesman.

Officials said the plant was undergoing a planned shutdown when something malfunctioned in their sulfuric acid system. The gas released turns into sulfur dioxide once it hits air, authorities said.

Fire officials said 27 workers were transported by ambulance to hospitals for treatment for non-life-threatening respiratory distress. Another 30 people were treated at the scene for minor inhalation problems.

Evacuated workers spent hours at a nearby park waiting for the all-clear, which was given at about 1 p.m.

"It kind of freaks you out," an unidentified worker said.

The weather did not help the situation.

"The wind was blowing from the northwest to the south, southeast. We called for a shelter-in-place," Newhouse said.

The shelter-in-place issued for the surrounding neighborhoods, Alta Academy and Davila and J.R. Harris elementary schools was lifted at 11:25 a.m.

The school lockdown created panic among some parents.

"I tried to get my kids out of there and they won't let me," a parent said.

No one outside the plant was injured.

Officials said the refinery manufactures diesel and jet fuels.

A portion of Manchester Street near Broadway Street was closed to traffic during the incident.